1. Field of the Invention
This invention relates to a sheet sorter. More particularly, to a sheet sorter in which printed or typed sheets are fed one by one from a printing or copying machine successively to a plurality of bin trays through a sheet feed passage which is suitably synchronized with the bin trays.
2. Description of the Related Art
A conventional sheet sorter known in the prior art includes a plurality of bin trays situated adjacent to an outlet from which sheets are fed one by one. The bin trays are stacked in a pile with gaps between adjacent bin trays, and the sheets are fed one by one to successive bin trays.
To align the outlet of the sheet feed passage successively with the gap between the adjacent bin trays, two solutions have been proposed, i.e., one in which the sheet feed passage is fixed, while the respective bin trays are shifted up and down, successively, and another in which the sheet feed passage is shiftable up and down, and the bin trays are fixed. Recently, however, a sheet sorter was proposed in which both the sheet feed passage and the stacked bin trays are shiftable in synchronization with each other.
In this kind of sheet sorter, due to the mutual movement of both the sheet feed passage and the bin trays, if a sheet once received in any one of bin trays happens to slip back toward the sheet feed passage, the rear edge of the sheet may, for example, become jammed in the normal sheet feed passage.
To overcome this kind of problem, in a sheet sorter, such as disclosed in U.S. Pat. No. 4,478,406, each of the bin trays has an up-right rear edge substantially perpendicular to a sheet receiving face of the bin tray, so that the sheet once received by the bin tray is prevented from moving backward because the rear edge of the sheet is held by the up-right rear edge portion of the bin tray.
However, this solution is not completely satisfactory, in that, if the sheet fed from the sheet feed passage to the bin tray is curled or electrostatically charged, then the sheet may be placed on the bin tray having a curvature of the sheet caused by feed rollers arranged adjacent to the outlet of the sheet fed passage, and such a sheet may be rolled up by or caught in the feed rollers.